Description / Abstract:
This standard covers the basic requirements for a corrosion
resistant non-electrolytically applied zincrich coating. Besides
corrosion protection, the coating also provides consistent
frictional properties.
Material Description. This
coating specification covers zinc flake coating with or without a
top coat.
Coating Types: Three levels of
corrosion protection are provided by the following types:
Type A: High corrosion resistant coating.
Type B: Medium corrosion resistant coating.
Type C: Low corrosion resistant coating. Note:
When not explicitly specified, the default coating type shall be
Type A. Parts contracted and Production Part Approval Processed
("PPAPed") before January 1, 2014, that is without the coating Type
(A, B, or C) specified, may continue to default to Type B.
Note: Type C coating systems may be without top
coat if coefficient of friction (CoF) requirements are met.
Treatment with an additional lubricant to meet CoF is
permissible.
Symbols. Not applicable.
Applicability. This coating is suitable for
externally and internally threaded fasteners size M6 or larger, and
other ferrous parts where high level of corrosion protection and
freedom from hydrogen embrittlement are required. This coating is
not recommended for the following types of parts:
- Bolts and nuts of sizes M6.
- Parts with internal drive recess and blind holes.
- Parts mating against magnesium surfaces.
- Loose washers of all sizes.
- Parts where electrical conductivity is
required.
Remarks.
This coating process does not generate hydrogen; however,
pre-treatment processes, i.e., acid pickling could cause hydrogen
adsorption.
Non-electrolytically applied zinc-rich coating has high
permeability which allows effusion of hydrogen during curing which
might have been absorbed during acid pickling. See precautions in
Section 3.1.
Use of this coating system on threaded surface and/or bearing
surface of joints could affect the torque-tension relationship. It
is recommended that a torque-tension study of the fastener joint be
performed before releasing this finish on any new
application.
The corrosion performance is influenced by part geometry,
substrate material, and application process. The coating systems
approved to this specification were tested to meet all requirements
using common steel fasteners. For new designs, applications, and
parts with complex geometries or difficult to clean material such
as castings and powder metal, extra validation testing is highly
recommended.
This finish is suitable for service temperatures from -50 °C to
+120 °C. Applications outside of this temperature range shall be
reviewed with the responsible Materials Engineering organization
before usage.
Dip-spin coating is a bulk process. If parts are prone to
nesting, stick together (flat washers), or easily damaged by
mechanical tumbling, dipspin coating method is not recommended.
Alternatives include spray and dip-drain methods.
Shot blasting is not a preferred pre-treatment method for
internally threaded parts (nuts), nutwasher and bolt-washer
assemblies. If shot blasting is used, extra care shall be taken to
ensure shots are not trapped in the coated parts.
This coating is relatively soft, and is prone to "dusting". It
is expected that equipment handling high volumes of coated parts
(such as automated bolt feeders) will require regular cleaning to
remove the coating dust.
Non-electrolytically applied zinc-rich coating has high
permeability which allows effusion of hydrogen during curing which
might have been absorbed during acid pickling. See precautions in
Section 3.1.1.
Use of this coating system on threaded surface and/or bearing
surface of joints could affect the torque-tension relationship. It
is recommended that a torque-tension study of the fastener joint be
performed before releasing this finish on any new application.
The corrosion performance is influenced by part geometry,
substrate material, and application process. The coating systems
approved to this specification were tested to meet all requirements
using common steel fasteners. For new designs, applications, and
parts with complex geometries or difficult to clean material such
as castings and powder metal, extra validation testing is highly
recommended.
This finish is suitable for service temperatures from -50 °C to
+120 °C. Applications outside of this temperature range shall be
reviewed with the responsible Materials Engineering organization
before usage.
Dip-spin coating is a bulk process. If parts are prone to
nesting, stick together (flat washers), or easily damaged by
mechanical tumbling, dipspin coating method is not recommended.
Alternatives include spray and dip-drain methods.
Shot blasting is not a preferred pre-treatment method for
internally threaded parts (nuts), nutwasher and bolt-washer
assemblies. If shot blasting is used, extra care shall be taken to
ensure shots are not trapped in the coated parts.
This coating is relatively soft, and is prone to "dusting". It
is expected that equipment handling high volumes of coated parts
(such as automated bolt feeders) will require regular cleaning to
remove the coating dust.